Polymeric sheets and films are used in a wide variety of configurations for a wide variety of purposes including as, for example, protective coverings and wraps, drop cloths, the backing member in adhesive tapes, etc.
Especially for sheets and adhesive tapes used in paint masking, it is required that the sheet or adhesive tape be readily torn by hand in order to provide desired degree of hand applicability and utility. Common masking tapes employ paper backings, which despite having been impregnated with saturants and binders to provide water resistance and stretchability still exhibit undue moisture sensitivity and are difficult to process with water-based coatings. Such tape backings also exhibit moisture instability such as cockling, buckling and shredding in certain operations such as wet sanding. Other common adhesive tape backings are based on polymer films which, while providing good strength, stretch and water resistance, are often difficult to tear easily by hand. In particular, films based on oriented polymers and especially oriented polyolefins are well known as adhesive tape backings, but usually require the use of a cutting blade or knife in order to be used. This is not desirable or of sufficient ease of use for many applications.
It has been found previously (e.g., U.S. Pat. No. 7,037,100 (Strobel et al.)) that using a process of rapidly heating an oriented polymer film wrapped on a tooled cooling roll can produce perforations in the film, allowing it to be readily torn by hand. Such films are thought to perforate due to the differential or localized nature of the heating of the film; the major film surface facing the heat source is exposed to a very high heat flux compared to the opposing surface of the film which is in contact with a cooled tooling roll. In the tooled roll, depressions forming the desired tear pattern act as thermal insulators to allow local specific heating of the corresponding areas of the film above the depressions, which causes the film to open producing perforations. The heat source is most advantageously provided by using an open flame burner which produces a high heat flux. Other heat sources can be used.
It has been known to make, using oriented precursor films that are capable of thermally-induced elastic recovery, films having modification zones comprising a rim portion surrounding a central opening, the modification zones surrounded by a land portion, wherein the thickness of the rim portion is greater than the thickness of the land portion, can be produced. As reported in International Publn. No. 2015/100319 (Strobel et al.) , such films, when used as the backing member of adhesive tapes, can provide good unwind and release performance without use of additional release agents and liners, good hand tearability, conformability, etc. Accordingly, such films and the resultant tapes incorporating them as backing members have numerous advantageous uses. However, because the central opening within each modification zone passes completely through the film, such films are inherently permeable.
The need exists for impermeable films and articles incorporating such films (e.g., adhesive tapes) that exhibit good release properties (and thus impart good unwind performance to an adhesive tape made with such films), good conformability, and hand tearability with other desired mechanical properties.